The present invention relates to an intraocular lens for use as a replacement for the natural lens of a human eye.
As an aid in understanding the present invention, background discussion will be given. As illustrated in FIG. 1, a sectional view of a normal eye, the wall 20 of the eyeball has a clear anterior or front portion 22, known as the cornea. The iris 24, a colored annular structure, is disposed posteriorly of cornea 22. The space 25 in front of the iris and behind the cornea is referred to as the anterior chamber. Iris 24 defines a hole or pupil 26 aligned with cornea 22 on the anterior-posterior (front to back) axis 28 of the eyeball. A clear, gelatinous substance known as vitreous is disposed in a cavity 29 posterior of the iris. A lens 30 including a nucleus 31 and a cortex 32 is disposed in the posterior chamber 33, the space between vitreous cavity 29 and iris 24. The lens is surrounded by a capsule consisting of the anterior capsule 34, a clear membrane overlying the anterior surface of lens 30, and the posterior capsule 35, a clear membrane overlying the posterior surface of lens 30, with posterior capsule 35 confronting vitreous cavity 29. Anterior capsule 34 and posterior capsule 35 are connected to the ciliary sulcus 36, a structure on the wall 20 of the eyeball immediately behind iris 24.
In the normal eye, light enters through cornea 22, passes through anterior chamber 25 and pupil 26 and is focused by lens 30 to form an image on retina 37, a light-sensitive tissue lining the rear portion of the eyeball. The retina converts this image into nervous impulses which are transmitted to the brain. The disease known as cataract occurs when either the lens or the capsule becomes clouded or opaque. This interferes with transmission of light to the retina and hence interferes with vision. The only known cure for cataract is to remove the affected tissue. In an "intracapsular" surgical technique, anterior capsule 34, lens 30 and posterior capsule 35 are removed. In an "extracapsular" procedure, only lens 30 and anterior capsule 34 are removed, posterior capsule 35 being left in place within the eye. Many ophthalmologists have been trained only in the intracapsular technique and therefore prefer this technique over the extracapsular technique. The extracapsular technique cannot be utilized if the posterior capsule is diseased or is damaged during surgery.
Once the lens has been removed from the eye, light entering the eye will not be properly focused on the retina without some artificial aid. Such aid can be provided by eyeglasses or contact lenses, but these aids do not provide satisfactory vision correction, comfort and convenience in all cases. Intraocular lenses, which can be surgically implanted within the eye, provide an alternative to eyeglasses and contact lenses.
As generally utilized in the ophthalmologic art, and as utilized herein, the term "intraocular lens" refers to an assembly including both a light focusing element or "optic" and ancillary structures which serve to anchor the optic in place within the eye. Presently available intraocular lenses are commonly categorized as either "anterior chamber," "iris supported" or "posterior chamber." Anterior chamber lenses, designed for placement within the anterior chamber of the eye, ordinarily incorporate rigid supporting structures. When the lens is in place within the eye, such supporting structures are engaged with the eye wall at the juncture of the cornea and the iris to retain the lens in position within the eye. As anterior chamber lenses do not depend upon the capsule to retain them in position within the eye, anterior chamber lenses can be implanted in the eye after an intracapsular extraction procedure, the extraction procedure most familiar to the majority of ophthalmologists. Accordingly, anterior chamber lenses have been widely utilized. However, the rigid supporting structures of anterior chamber lenses must be provided in numerous different sizes to accommodate eyes of various sizes. Moreover, either the optic or the supporting structures of an anterior chamber lens may irritate the cornea.
Iris supported lenses ordinarily incorporate an optic and a plurality of filamentary supports. When the lens is implanted in the eye, the optic is disposed in the anterior chamber, the supports extending through the pupil and radially outwardly along the posterior surface of the iris. Because the iris is engaged between the posterior surface of the optic and the supports, the iris retains the lens in position within the eye. However, this iris can become disengaged from between the optic and the supporting elements upon extreme dilation of the pupil, thus leaving the lens free to move within the eye. In an attempt to alleviate this problem, some iris-supported lenses have been provided with additional supports arranged to extend outwardly from the optic along the anterior surface of the iris. Also, iris-supported lenses have been provided with staves, spikes or sutures extending through the iris to more firmly anchor the optic thereto. Despite such added features, many surgeons prefer to implant iris-supported lenses only when the posterior capsule remains intact within the eye so that scar tissue can firmly attach the supports of the lens to the posterior capsule and anchor the lens in place. This preference, in turn, dictates the employment of an extracapsular procedure for removing the natural lens. This has been an important deterrent to the use of iris-supported lenses. Moreover, if the capsule itself is diseased and must be removed, an extracapsular procedure cannot be utilized. Further, because the optic of an iris-supported lens is positioned in the anterior chamber, the optic can scratch the cornea.
In recent years, posterior chamber lenses have become more widely accepted. The optic of a posterior chamber lens is disposed in the posterior chamber when the lens is implanted. Because the optic is remote from the cornea, the posterior chamber lens generally does not produce corneal irritation. However, the posterior chamber lenses available heretofore have generally depended on the posterior capsule for fixation of the lens within the eye. Accordingly, such lenses have required the use of an extracapsular surgical technique which leaves the posterior capsule intact. For example, the most widely adopted posterior chamber lens heretofore has been the so-called Shearing lens. This lens has two J-shaped resilient support members extending from its optic. The support members engage the wall of the eye of the ciliary sulcus immediately posteriorly of the iris and effectively retain the optic against decentration or movement transversely of the axis of the eye. However, the support members do not provide any substantial support against movement of the optic posteriorly within the eye. Accordingly, the posterior capsule must remain intact if this lens is utilized.